Hard Projectiles Research Articles

Development of an ultrahigh strength low alloy steel for armour applications

The present paper describes a steel with yield strength exceeding 1900 MPa and fracture toughness in the range of 40–50 MPa m1/2, in its optimum heat treated condition. Its strength is similar to that of 18 Ni (300) grade of maraging steel with good fracture toughness. When tempered at 300°C, it shows tempered martensite along with a small amount of retained austenite phase. The steel shows nearly 25% reduction in weight over typical rolled homogeneous armour (RHA) steel against high velocity hard steel core projectiles. The processing, microstructure, mechanical and ballistic properties of the steel are demonstrated.

Effect of projectile hardness on deformation and fracture behavior in the Taylor impact test

The ballistic perforation performance of a kinetic energy projectile would be much more influenced by the projectile’s deformation during the impact process. A projectile may suffer from large deformation and even fracture as more and more advanced materials are used as resistant components. A comparison investigation was presented in this study concerning the deformation and fracture behavior of kinetic energy projectiles manufactured from 38CrSi steel of two different hardness values. Flat-nosed projectiles were fired in a two-stage compressed gun test facility against hard steel plates within the velocity range of 200–600 m/s. The impact process was monitored by a high-speed camera. Experimental results showed that, for the soft projectiles there are three deformation and fracture modes, i.e., mushrooming, shear cracking and petalling, and that for the hard projectiles there are also three modes, mushrooming, shearing cracking and fragmentation.

10.1007/s11455-008-2005-7

It is established that single-crystalline brittle materials exhibit a lower resistance to the penetration of hard projectiles as compared to analogous polycrystalline targets with the same composition and standard mechanical properties. This difference is explained by the fact that single crystals, in contrast to polycrystalline materials, exhibit a significant decrease in hardness in the initial stage of impact as compared to the value measured under standard conditions.

Investigation on penetration resistance of foamed concrete

This paper studies the penetration resistance of lightweight foamed concrete subjected to impact by hard projectiles. Experiments were performed to obtain the mechanical properties of the material and the penetration depth. Complete stress–strain curves in compression are presented, based on which several important parameters for the description of the compressive strength and energy absorption of the foamed concrete were determined. The penetration depths of hard projectiles were measured at various impact velocities between 10 m/s and 150 m/s with different types of projectile nose shapes including flat, cone and spherical noses. A simulation model based on rigid body dynamics and a shock resistance function is proposed to predict the penetration depth. Reasonably good agreement between experimental and simulating results is achieved.

Resistance of brittle solids to high-velocity projectile penetration at the initial stage of impact

It is established that single-crystalline brittle materials exhibit a lower resistance to the penetration of hard projectiles as compared to analogous polycrystalline targets with the same composition and standard mechanical properties. This difference is explained by the fact that single crystals, in contrast to polycrystalline materials, exhibit a significant decrease in hardness in the initial stage of impact as compared to the value measured under standard conditions.

Mechanisms governing the high temperature erosion of thermal barrier coatings

The impact of thermal barrier coatings by hard projectiles at high temperature has been analyzed. Three different domains have been explored: each differentiated by particle size, velocity, temperature and TBC composition. Domain I applies when the projectile creates deeply penetrating plastic/densification zones. In this case, short time elastic effects are relatively unimportant. The response is dominated by stresses that arise after about 1 ms, at particle rebound. Deformation incompatibilities nucleate delaminations: which thereafter, extend in the TBC just above the interface with the TGO. An index governing material removal by delamination has been derived as Ξ 1= Γ TBC E TBC 2/( σ Y TBC) 3, where Γ TBC is the toughness of the TBC, E TBC its Young’s modulus and σ Y TBC its yield strength. In Domain II the plastic wave intensity is below the delamination threshold: whereupon a thin densified zone is formed, without severe cracking. Subsequent impacts induce elastic bending of the neighboring columns. The bending develops at short times (10–50 ns), causing large, transient stresses at the intersection between the dense and underlying columnar layers. These stresses can be large enough to form cracks that remove the dense layer. Analysis of this effect identifies an erosion index: Ξ 2≡Γ TBC /E TBC 3/5 dσ Y TBC , where d is the column diameter. Large values of Ξ 2 reduce the erosion rate. Domain III arises for impact conditions that elicit an entirely elastic response in the TBC. The domain applies at low temperature and when the impacting particles are small. Again, bending effects at the tops of the columns arise at short times. Another erosion index arises, Ξ 3≡Γ TBC /E TBC 3/5 d , differing from that in Domain II because plasticity is not involved.

Dynamic strains in architectural laminated glass subjected to low velocity impacts from small projectiles

An experimental validation of a mechanics-based finite element model for architectural laminated glass units subjected to low velocity, two gram projectile impacts is described. The impact situation models a scenario commonly observed during severe windstorms, in which small, hard projectiles, such as roof gravel, impact windows. Controlled experiments were conducted using a calibrated air gun to propel a steel ball against simply supported rectangular laminated glass specimens. Dynamic strains on the inner glass ply were measured using foil strain gages and a high speed data acquisition system. Impact speed, interlayer thickness, glass ply thickness, and glass heat treatment conditions were varied. Dynamic strains predicted by the finite element model were in close agreement with those measured in the laboratory.